Transcript Lecture 3 Sulphonamides 2012 (2)

Sulphonamides
Dr. Anuradha nischal
 synthetic
simply
 Primarily
Cellular
antimicrobial agents
called sulfa drugs
Bacteriostatic drugs
& humoral immunity of host is
essential for eradication of the infection.
Spectrum
Gram positive & Gram negative
Emergence of resistance
Usefulness has declined
Susceptible microorganisms:

 Streptococcus
pyogenes
 Streptococcus pneumoniae

Nocardia, Actinomycetes, Calymmato
bacterium granulomatis & Chlamydia
trachomatis
 H.
influenzae
 H. Ducreyi
Organisms now Resistant
 N. Meningitidis - Serogroups A, B,
&C
 Shigella
 E.Coli
Mechanism
of action
 Competitive
inhibitors of
dihydropteroate synthase
bacterial enzyme responsible for
the incorporation of PABA into
dihydropteroic acid
immediate precursor of folic acid.
Pteridine + PABA/
..
sulpho
Dihydropteroate synthase
Dihydropteroic acid
Dihydrofolic acid
Dihydrofolate reductase
Tetrahydrofolic acid
 Folic
acid is used for the synthesis of
purines and thymine
Required
for formation of DNA
Therefore folic acid is required for
replication of cellular genes.
 Important
function of folic acid is to
promote growth so in its absence
organism grows very little.
Sulfonamides are
 Also

k/a anti-metabolites
i.e. They block the essential enzymes of
folate metabolism.
Mechanism of action
 Structural
analogues of PABA (paraamino benzoic acid)
 Sulfonamide gets incorporated to form
an altered folate which is
metabolically injurious.
Sensitive micro-organisms are those that must
synthesize their own folic acid. Bacteria that
can use preformed folate are not affected.
 Bacteriostasis induced by sulfonamides is
counteracted by PABA competitively.

 Pus
rich in PABA
 Efficacy is lost

Mammalian cells are not affected, they require
preformed folic acid and cannot synthesize it
Absorption, Fate & Excretion

Absorbed rapidly from GIT
 Small
intestine(major site) & stomach
PPB variable, albumin,
 Distributed throughout the body

 Readily
enter pleural, peritoneal, synovial,
ocular fluids
 Conc. 50-80% that in blood
Readily cross placenta (antibacterial +
toxic effects)
 Metabolised in liver,
 Excreted in urine
Small amounts in faeces, bile, milk and
other secretions.

Classification
Agents that are absorbed & excreted
rapidly
 Sulfisoxazole
 Sulfamethoxazole
 Sulfadiazine
 Agents that are absorbed very poorly
when administered orally, hence active
in bowel lumen
 Sulphasalazine

Long acting sulphonamides absorbed
rapidly excreted slowly
 Sulfadoxine
 Agents used topically
 Sulfacetamide
 Mafenide
 Silver sulfadiazine

Pharmacological properties of
Individual Sulphonamides
Sulfisoxazole
Rapidly absorbed & excreted sulfonamide
with excellent antibacterial activity
 Half life 5-6 hrs
 High solubility, no crystalluria
 Replaced less soluble agent.
 Bactericidal activity in urine.

Sulfisoxazole acetyl
 Tasteless

– oral use in children
erythromycin
ethylsuccinate for children with otitis
media.(phenazopyridine in mixture(UA &
Fixed dose combination with
analgesic; urine red.)
Sulfamethoxazole
 Close
congener of sulfisoxazole
 Half-life :8-12 Hrs
 Fixed dose combination with
trimethoprim
 High fraction is acetylated, which is
relatively insoluble crystalluria can occur.
 Precautions
to avoid crystalluria
Poorly absorbed sulfonamides
Sulfasalazine

poorly absorbed from GIT
 Active
in bowel lumen
 Ulcerative collitis, regional enteritis
Intestinal bacteria - sulfapyridine (toxic)
+ 5 aminosalicylate (effective agent in IBD)

Sulfonamides for topical use
Sulfacetamide

Extensively-management of Opthalmic
infections (Trachoma/Inclusion
conjunctivitis)
 Penetrates
ocular fluids & tissues in high
concentrations.
 Advantage: very high aqueous conc. not irritating to
eyes & are effective against susceptible
microorganisms.

Sulfacetamide sodium 10-30%
Silver Sulfadiazine
 Inhibits
growth of nearly all pathogenic
bacteria & fungi
 Used topically to reduce incidence of
infections of wounds from burns
Slowly
releases silver ions
-
antimicrobial action
DOC
for prevention of infection of burns.
Mafenide
of colonization of burns
by a variety of gram negative & gram
positive bacteria
 Prevention
Limited
usefulness: inhibits carbonic
annhydrase metabolic acidosis
LONG ACTING SULFONAMIDES
Sulfadoxine



Long acting
Half-life :7-9 days
Combination
Sulfadoxine 500mg + Pyrimethamine 25 mg
Prophylaxis & treatment of malaria caused by
chloroquine resistant strains of plasmodium
falciparum.
Falciparum Malaria
 Pyrimethamine
 Inhibits

Plasmodial DHFRase
Supraadditive synergistic combination with
pyrimethamine due to sequential block
 Combination
acts faster
 Development of resistance to pyrimethamine is
retarded.
Clinical curative
 Three tablets single dose
 Both long half-life
Advantage of combination
 Good compliance due to single dose
therapy

Resistance to sulfonamides

Resistant mutants
 Produce
increased amounts of PABA
 Their Folate synthetase enzyme has low
affinity for sulfonamides
 Adopt alternate pathway of folate metabolism.
Crystalluria
Older, less soluble sulphonamides
 Insoluble in acidic urine
 Precipitate, forming crystalline deposits
that can cause urinary obstruction.

Fluid intake sufficient to ensure a daily
urine volume of at least 1200ml
 Alkalinization of the urine if pH low
 Sulfisoxazole more soluble, incidence of
this problem is low

kernicterus
 Administration
to newborn infants esp.
premature
Sulfonamides
displace bilirubin from plasma
albumin.
Free bilirubin is deposited in basal ganglia &
sub-thalamic nuclei of the brain causing an
encephalopathy called kernicterus.
 Hypersenstivity
reactions
 Acute hemolytic anaemia in G6PD deficient patient
 Agranulocytosis
- sulfadiazine
 Aplastic anaemia
 Anorexia, nausea, vomiting

Potentiate the effect
Oral anticoagulants
Sulphonylurea hypoglycaemic agents
Hydantoin anticonvulsants
Inhibition of metabolism of these drugs +
displacement from albumin.
Dosage adjustment
 Cautious
use in patients with
impaired renal functions.

Urinary tract infections
 No
longer therapy of first choice
 Quinolones
 Co-trimoxazole
 Fosfomycin
 Ampicillin
 Urinary
antiseptics
 Nocardiosis
Sulfisoxazole/Sulphadiazine;
DOC
Complete
recovery with adequate treatment
6-8 g daily/80-160 µg/ml
Schedule continued for several months after
all manifestations have been controlled.
 Toxoplasmosis
Pyrimethamine-sulphadiazine
combination is Tt of choice
 Pyremethamine
loading dose- 75 mg
25 mg orally per day
 Sulphadiazine 1 g orally every 6 hrs.
 Folinic acid 10 mg orally every day.
For 3-6 weeks.
 2 litres of fluid intake daily.
 Prophylaxis
& treatment of malaria
 Prophylaxis of streptococcal infections
in patients hypersensitive to Penicillin.
DOC
is Penicillin.
Sulphonamides are as efficacious
Should be used without hesitation in patients
hypersenstive to penicillins
Topical uses

Used extensively in the management of
Opthalmic infections

Used topically to reduce incidence of
infections of wounds from burns, DOC.
 Ulcerative
collitis, regional enteritis
COTRIMOXAZOLE
Sulfameth
oxazole
Trimeth
oprim
Cotrimo
xazole
Sulfamethoxazole
competitive
inhibitors of
dihydropteroate
synthase
Trimethoprim
Trimethoprim
inhibitis
dihydrofolate
reductase
prevents
reduction of
dihydrofolate to
tetrahydrofolate
Pteridine + PABA
Dihydropteroate synthase
Dihydropteroic acid
Dihydrofolic acid
Dihydrofolate reductase
Tetrahydrofolic acid

Acts on Sequential steps
 Synergism

Two drugs interfere with two successive
steps in the same metabolic pathway&
produce supraadditive effect. (Sequential
blockade)
 Individually
both are bacteriostatic but
the combination has cidal effect
 Chances of development of bacterial
resistance are also greatly reduced
 Pk
properties of both the drugs
match closely
Synergism

Optimal ratio of the concentrations of the two
agents for Synergism 20:1
 Sulfamethoxazole
: Trimethoprim
Combination is formulated to achieve a
sulfamethoxazole conc. in vivo 20 times greater
than that of trimethoprim
Trimethoprim 20-100 times more potent
 Dose ratio
5:1; S: 800 mg; T: 160mg

Trimethoprim is a highly selective inhibitor of
DHFRase of lower organisms
 Approx. 1,00,000 times more drug is required to
inhibit human DHFRase than than bacterial
enzyme

 Do
not interfere with folic acid metabolism in human
beings

Mammalian cells preformed folate from the diet
Spectrum

Broad spectrum
 Both Gram negative & Gram positive
Combination:
Chlamydia, diptheriae, N. meningitidis
 S. aureus, S. pyogenes, proteus,
 Pneumocystis carinii,
 Salmonella typhi, shigella, Klebseilla,
 Resistance can develop when trimethoprim is
used alone


Resistance to co-trimoxazole is reportedly
formed in almost 30 % of urinary isolates
of E. coli.
Resistance
 Mutational
 Plasmid
mediated acquisition of altered
DHFRase having low affinity for
trimethoprim.
Adverse
effects
No evidenve of folate deficiency in normal
person at the recommended doses
 Folate deficiency can occur in patients
deficient in folate in diet:

 Megaloblastosis,
 leukopenia,
 thrombocytopenia,

Hypersensitivity reactions involving skin
 AIDS
patients frequently have hypersenstivity
reactions with co-trimoxazole
Nausea vomiting
 Glossitis
 Stomatitis
 CNS: headache ,depression, etc

Therapeutic
Uses
Urinary tract infections
 Uncomplicated lower urinary tract
infections
 Highly

effective for enterobacteriacae
S: 800 mg; T: 160mg;
2
tablets single dose; effective
 Minimum of 3 days therapy is more likely
to be effective.
Chronic & Recurrent UTI Women in
reproductive age group
 Post coitally.
S; 200 mg +T; 40 mg/day.
Or 2-4 times once/twice per week.
 Presence of trimethoprim in vaginal
secretions.
Bacterial prostatitis
 Presence of therapeutic concentrations of
trimethoprim in prostatitic secretions
Respiratory tract infections
 Acute & chronic bronchitis
Acute otitis media in children
 Acute maxillary sinusitis in adults d/t S.
pneumoniae & H. influenzae (if
susceptible)

GI tract infections
 Alternative to fluoroquinolone for
treatement of Shigellosis.
 Second line drug for typhoid fever.
 Seldom
used
 Ceftriaxone/ FQs preferred
Infection by Pneumocystis carinii/
jiroveci in neutropenic & AIDS patients
 Causes severe pneumonia in these
patients
 High dose therapy T-15-20
mg/kg/day,S-75-100 mg/kg/day is
effective for infection by pneumocystis
jiroveci infection in patients with AIDS.
 Miscellaneous:
 Nocardia
 Whipple’s disease
 Wegener’s granulomatosis
THANK
YOU